I wanted to make the garden light PIR activated, so have added this PIR
sensor from SparkFun.
Although the sensor has an input voltage of 5V to 12V DC, it actually runs at 3.3V. So, if you bypass the voltage regulator it will run using the battery in the garden light control unit. I powered the PIR up using 5V and then using my multimeter verified where to attach the new power feed.